Recently, conductive ink is drawing attention since it is useful in metal film or pattern formation and electrode printing in the field of lead (Pb) free electric/electronic circuits, low-resistance metal wirings, printed circuit boards (PCB), flexible printed circuit boards (FPC), antennas for radio frequency identification (RFID) tags, electromagnetic interference (EMI) shielding, plasma displays (PDP), liquid crystal displays (TFT-LCD), organic light emitting diodes (OLED), flexible displays and organic thin film transistors (OTFT).
Japanese Patent Laid-Open No. 2004-221006 (Aug. 5, 2004) and Japanese Patent Laid-Open No. 2004-273205 (Sep. 30, 2004) disclose conductive inks in the form of a paste prepared from nanoparticle, powder or flake of metal or metal alloy using a binder resin or a solvent. Chem. Mater., 15, 2208 (2003), Japanese Patent Laid-Open No. Hei 11-319538 (Nov. 24, 1999), Japanese Patent Laid-Open No. Hei 2004-256757 (Sep. 10, 2004) and U.S. Pat. No. 4,762,560 (Aug. 9, 1988) disclose the method of reacting such metal compounds as silver nitrate, hydrogen tetrachloroaurate and copper sulfate with other compounds in an aqueous solution or an organic solvent to form colloids or nanoparticles. However, these methods are uneconomical and less stable and require a complicated process. In addition, the high baking temperature makes them inappropriate to be applied for a variety of substrates.
Carboxylate is well known as a ligand that forms complexes, particularly organic metal complexes Prog. Inorg. Chem., 10, p. 233 (1968). In general, since metal carboxylate complexes are less soluble in organic solvents J. Chem. Soc., (A), p. 514 (1971), U.S. Pat. No. 5,534,312 (Jul. 9, 1996) and are discomposed at high temperature, they are limited in application in spite of easiness in preparation. Several methods have been proposed to solve this problem in J. Inorg. Nucl. Chem., 40, p. 1599 (1978), Ang. Chem., Int. Ed. Engl., 31, p. 770 (1992), Eur. J. Solid State Inorg. Chem., 32, p. 25 (1995), J. Chem. Cryst., 26, p. 99 (1996), Chem. Vapor Deposition, 7, 111 (2001), Chem. Mater., 16, 2021 (2004), U.S. Pat. No. 5,705,661 (Jan. 6, 1998), Japanese Patent Laid-Open No. 2002-329419 (Nov. 15, 2002) and Korean Patent Publication No. 2003-0085357 (Nov. 5, 2003). Of them are the methods of using a carboxylate compound with a long alkyl chain or using an amine compound or a phosphine compound.
The present inventors have presented stable and highly soluble complex compounds and preparation methods thereof in Korean Patent Application Nos. 2005-11475 and 2005-11478. Particularly, in Korean Patent Application Nos. 2005-18364 and 2005-23013, they presented stable and transparent conductive ink compositions with superior solubility and good conductivity, metal content of which and film thickness can be easily controlled, and methods for forming metal patterns easily even at low temperature using the compositions. However, a variety of conductive inks are required to produce high-quality specialty products or to meet the situation where special properties are needed.
According to Ullmann's Encyclopedia of Ind. Chem., Vol. A24, 107 (1993), silver is a precious metal which is not oxidized easily and has good electrical and thermal conductivity and catalytic and antibacterial activity, and thus silver and silver compounds are used widely in the industries, in silver alloys, plating, medicines, photographs, electric and electronic products, fibers, detergents, household appliances, etc. In addition, silver compounds can be used as catalyst in the synthesis of organic compounds and polymers. Particularly, silver is recently used in the new fields that require metal patterns or electrodes, including lead-free electric/electronic circuits, low-resistance metal wiring, PCBs, FPCs, antennas for RFID tags, EMI shielding, PDPs, TFT-LCDs, OLEDs, flexible displays and OTFTs.
Of recent, researches for replacing aluminum with silver, which has better reflection and conduction properties, in reflection film for reflection type or semi-transparent type LCDs are in progress, as disclosed in Japanese Patent Laid-Open No. 2002-129259 (May 9, 2002), Japanese Patent Laid-Open No. 2004-176115 (Jun. 24, 2004) and Japanese Patent Laid-Open No. 2004-231982 (Aug. 19, 2004).
However, compounds derived from silver are limited and they lack stability and solubility. In addition, they have a decomposition temperature of 200° C. or higher, which is too high to obtain a metal pattern with good conductivity, and are decomposed slowly.
The present inventors have worked consistently to solve these problems and come to complete this invention. The present invention provides a conductive ink composition having very superior stability and solubility, enabling easy formation of thin film and being easily calcined even at low temperature, thereby enabling formation of uniform and precise film or pattern with good conductivity regardless of the particular substrate used, and a method for preparing the same.